Proposed studies are designed to investigate the toxicological effects of an organomercurial, viz., methylmercuric hydroxide, on cells and cellular components. Specifically, proposed research will be concerned: (1) with the investigaton of the methylmercury-induced changes in the cell cycle events of mammalian cell cultures using cytological characterization techniques as well as biochemical isolation and fractionation procedures in an attempt to obtain information with respect to the "target" of the action of the organomercurial. (2) with the study of the physical and chemical properties of the methylmercury complexes of chromatin (interphase chromosomes) and its associated proteins (histones) using physico-chemical methods such as circular dichroism measurements, ultraviolet spectrophotometry, column chromatography, and gel electrophoresis as characterization techniques. The interphase chromosomes serve hereby as models of possible "target" molecules for organomercurials at the molecular level. BIBLIOGRAPHIC REFERENCES: J.C.C. Fu and D.W. Gruenwedel, Salt Effects on the Denaturation of DNA. V. Preferential Interactions of Native and Denatured Calf Thymus DNA in Na2SO4 Solutions of Varying Ionic Strength, Biopolymers 15, 265-282 (1976). V.C.W. Chu and D.W. Gruenwedel, On the Hg(II)-Induced Dealkylation of Methylcobalamin, Bioinorg. Chem. (1977) (in press).